Gerard Hamill

The decay of maximum velocity within the initial stages of a propeller wash

The velocity characteristics of the submerged jet produced by a rotating ship propeller are described in terms of the maximum velocity measured on the propeller plane. Detailed measurements of velocities have been taken in the zone of the wash close to the propeller. The maximum velocity has been found to decay with distance from the propeller source. The maximum velocity in the zone of formation of the propeller jet has been shown to depend upon the efflux velocity and the blade area ratio for the propeller.

A METHOD FOR ESTIMATING THE BED VELOCITIES PRODUCED BY A SHIP'S PROPELLER WASH INFLUENCED BY A RUDDER

Detailed studies have been undertaken to assist in the design of major extensions to the port of Haifa. Both numerical and physical model studies were done to optimise the mooring conditions vis a vis the harbour approach and entrance layout. The adopted layout deviates from the normal straight approach to the harbour entrance. This layout, together with suitable aids to navigation, was found to be nautically acceptable, and generally better with regard to mooring conditions, on the basis of extensive nautical design studies.Hwa-Lian Harbour is located at the north-eastern coast of Taiwan, where is relatively exposed to the threat of typhoon waves from the Pacific Ocean. In the summer season, harbour resonance caused by typhoon waves which generated at the eastern ocean of the Philippine. In order to obtain a better understanding of the existing problem and find out a feasible solution to improve harbour instability. Typhoon waves measurement, wave characteristics analysis, down-time evaluation for harbour operation, hydraulic model tests are carried out in this program. Under the action of typhoon waves, the wave spectra show that inside the harbors short period energy component has been damped by breakwater, but the long period energy increased by resonance hundred times. The hydraulic model test can reproduce the prototype phenomena successfully. The result of model tests indicate that by constructing a jetty at the harbour entrance or building a short groin at the corner of terminal #25, the long period wave height amplification agitated by typhoon waves can be eliminated about 50%. The width of harbour basin 800m is about one half of wave length in the basin for period 140sec which occurs the maximum wave amplification.Two-stage methodology of shoreline prediction for long coastal segments is presented in the study. About 30-km stretch of seaward coast of the Hel Peninsula was selected for the analysis. In 1st stage the shoreline evolution was assessed ignoring local effects of man-made structures. Those calculations allowed the identification of potentially eroding spots and the explanation of causes of erosion. In 2nd stage a 2-km eroding sub-segment of the Peninsula in the vicinity of existing harbour was thoroughly examined including local man-induced effects. The computations properly reproduced the shoreline evolution along this sub-segment over a long period between 1934 and 1997.In connection with the dredging and reclamation works at the Oresund Link Project between Denmark and Sweden carried out by the Contractor, Oresund Marine Joint Venture (OMJV), an intensive spill monitoring campaign has been performed in order to fulfil the environmental requirements set by the Danish and Swedish Authorities. Spill in this context is defined as the overall amount of suspended sediment originating from dredging and reclamation activities leaving the working zone. The maximum spill limit is set to 5% of the dredged material, which has to be monitored, analysed and calculated within 25% accuracy. Velocity data are measured by means of a broad band ADCP and turbidity data by four OBS probes (output in FTU). The FTUs are converted into sediment content in mg/1 by water samples. The analyses carried out, results in high acceptance levels for the conversion to be implemented as a linear relation which can be forced through the origin. Furthermore analyses verifies that the applied setup with a 4-point turbidity profile is a reasonable approximation to the true turbidity profile. Finally the maximum turbidity is on average located at a distance 30-40% from the seabed.

Determining Propeller Erosion at the Stern of a Berthing Ship

AbstractThis paper presents the findings from an experimental investigation into the nature and extent of the scouring that occurs when a ship berths in front of a perpendicular quay wall within the confines of a harbor. It examines the interaction between the relative position of the quay wall to the central axis of the ship and the influence of the angle of the vessel’s rudder on the magnitude of the scouring produced. The experimental program covered a range of sediment sizes, propeller diameters and speeds of rotation, and rudder angles. Also, methods for calculating the depth of expected scour are presented in terms of initial semiempirical equations for the data range under investigation.

An Experimental Investigation Of SalineIntrusion In A Long Sea Outfall

The discharge and subsequent dispersion of wastewater through long sea outfalls is often inhibited by the intrusion of saline receiving water into the outfall diffiiser. Until recently, numerical modelling of intrusion and purging of saline water has been limited to one-dimensional (1-D) and enhanced 1-D models, which do not adequately describe the complex hydrodynamic processes generated within these devices. Recent research [1] has resulted in the development of a two-dimensional (2-D) numerical model to simulate the internal hydraulics of a long sea outfall with a saline intrusion. The model, which was developed using the FLUENT computational fluid dynamics (CFD) package, is designed to reproduce the effects of buoyancy and stratification, so that the interaction between the saline sea water and the effluent may be more accurately predicted. In this paper, details of an experimental investigation to assess the performance of the numerical model are presented. The investigation used a 1 in 30 scale model of a typical modern outfall difiuser discharging, under simplified conditions, into still receiving waters. Information is provided on model scaling, experimental facilities, instrumentation, and measurement procedures. The paper documents the results of an initial test series, in which discharge was permitted through only one of the outfalls four vertical risers. The results include measurements of velocity and water density within the model outfall as the conditions change from a steady state with the outfall fully intruded, through the transitory purging period, to normal operation. A brief overview of the numerical modelling technique is provided and a comparison of the results obtained using the physical and numerical models is presented. Advances in Fluid Mechanics III, C.A. Brebbia & M. Rahman (Editors)

Transient Investigation of the Critical Abstraction Rates in Coastal Aquifers: Numerical and Experimental Study

This research investigated the transient saltwater upconing in response to pumping from a well in a laboratory-scale coastal aquifer. Laboratory experiments were completed in a 2D flow tank for a homogeneous aquifer where the time evolution of the saltwater wedge was analysed during the upconing and the receding phase. The SEAWAT code was used for validation purposes and to thereafter examine the sensitivity of the critical pumping rate and the critical time (the time needed for the saltwater to reach the well) to the well design and hydrogeological parameters. Results showed that the critical pumping rate and the critical time were more sensitive to the variations of the well location than the well depth. The critical time increased with increasing the location and depth ratios following a relatively linear equation. For all the configurations tested, the lowest critical pumping rate was found for the lower hydraulic conductivity, which reflects the vulnerability of low permeability aquifers to salinization of pumping wells. In addition, higher saltwater densities led to smaller critical pumping rate and shorter critical time. The influence of the saltwater density on the critical time was more significant for wells located farther away from the initial position of the interface. Moreover, increasing the dispersivity induced negligible effects on the critical pumping rate, but reduced the critical time for a fixed pumping rate.

An Advanced Calibration Method for Image Analysis in Laboratory-Scale Seawater Intrusion Problems

Image analysis is a useful tool for visualising flow through laboratory-scale aquifers but existing methods of converting image light intensity to concentration can be labour intensive and time consuming. The new approach proposed in this study utilises the Random Forest machine learning technique to build a calibration model to replace the requirement for unique calibrations of each test aquifer. Calibration images from a previous experimental study were used to train the Random Forest model and the output was compared to the results from a high resolution pixel-wise methodology. The Random Forest model provided a trade-off in accuracy with increased efficiency and reduced sensitivity to image desynchronisation when compared to the pixel-wise method. The reduced accuracy was attributed in part to non-linear lighting distribution across the sandbox, which could be corrected by orientating the backlights effectively. Time savings of around 35% were achieved for this experimental study and this is expected to increase for larger scale studies. The new calibration approach exhibits some promising features in terms of its robustness to experimental error and its ability to process efficiently large-scale experiments in a shorter time frame.

Development Of A Numerical Model To SimulateWave Induced Flow Patterns Within A Long SeaOutfall

Since their installation, long sea outfalls have suffered from saline intrusion. This migration of the receiving water into the outfall diffuser leads to reduced operational efficiency due to partial blockage of the system. Wave induced saline intrusion is a common phenomenon in shallow receiving waters. It is widely believed that the geometry of the outfall has a significant effect on the onset of wave induced intrusion. However, to date, a satisfactory method of assessing the influence of waves on the internal hydraulics of outfall diffusers of differing geometries has not been achieved. This document presents details of a two-dimensional numerical model to simulate sinusoidal wave generation in an open water body. The model is based on the FLUENT computational fluid dynamics (CFD) software and uses the volume of fluid (VOF) method to model the free surface flow. Simple geometrical structures, such as that of an outfall difiuser, can also be incorporated within the flow domain. The purpose of the model is to allow prediction of the wave-induced pressures and velocities generated within long sea outfalls or other open submerged pipes or ducts in a marine environment. The model permits investigation of the internal hydraulics of such systems and allows the geometrical configuration of a structure to be varied and the resulting flow patterns to be examined This study concentrates on the modelling of a simple parallel plate duct to enable the numerical model to be validated before more complex geometries are used. In this paper the results obtained from experimental and computational modelling of a submerged duct are presented. Comparisons of theoretical waveinduced velocities and numerical predictions are discussed. Advances in Fluid Mechanics III, C.A. Brebbia & M. Rahman (Editors)